[3-(Aminomethyl-hydroxy-phosphinoyl)-propionylamino]-acetic acid or its ester compounds (I) and their salts are new. [3-(Aminomethyl-hydroxy-phosphinoyl)-propionylamino]-acetic acid or its ester compounds of formula (R 1-NH-CH(R 2)-P(=O)(OR 3)-CH 2-C(R 4)(R 5)-CONH-CH(R 6)-COOR 7) (I) and their salts are new. R 1 : -C(=O)-O-C(R 8)(R 9)-OC(=O)-R 1 0； either R 8, R 9 : H or T； or CR 8R 9 : saturated 5 or 6 membered hydrocarbon ring； R 1 0 : T； T : alkyl, aryl, arylalkyl, cycloalkyl, cycloheteroalkyl, heteroalkyl, heteroalkyl, heteroaryl or heteroarylalkyl； R 2 : optionally saturated 1-6C hydrocarbon (optionally substituted by OR 1 1, SR 1 1, SOR 1 1, amino, or phenyl (optionally substituted by halo, preferably F)), heteroaryl, aryl (preferably phenyl optionally substituted by F), or methylene group substituted by a 5 or 6 membered heterocycle optionally saturated or aromatic, containing heteroatoms of S or N, optionally oxidized form of N-oxide or S-oxide； R 3 : H, or group of formula (C(R 1 3)(R 1 2)-OC(=O)-R 1 4)； R 1 1 : H, benzyl or optionally saturated 1-4C hydrocarbon； either R 1 2, R 1 3 : H or T； or CR 1 2R 1 3 : 5 or 6 membered hydrocarbon ring； R 1 4 : T； either R 4 : benzyl or phenyl (optionally substituted by 1-5 halo (preferably Br or F), OR 1 5, SR 1 5, amino, CF 3, phenyl or 5 or 6 membered heteroaromatic ring), 5 or 6 membered heteroaromatic ring (comprising 1 or 2 heteroatoms of O, N or S and nitrogen can be oxidized form of N-oxide), or methylene group substituted by a 5 or 6 membered heterocycle optionally saturated or aromatic, containing one or more heteroatoms of S or N, optionally oxidized form of N-oxide or S-oxide； and R 5 : H； or CR 4R 5 : 5 or 6 membered hydrocarbon ring, or piperidine ring, where nitrogen is present in position 4, (optionally substituted by phenyl or benzyl (both optionally substituted by halo, 1-4C alkyl or 1-4C alkoxy), or aromatic heterocycle such as pyridine or pyrimidine (optionally substituted by 1-4C alkyl or 1-4C al
